1. Field of the Invention
This invention relates to graft copolymers and particularly plastic graft copolymers having polyamide side chains on active sites of an ethylene-containing trunk copolymer.
2. Description of the Prior Art
Graft copolymers are materials having trunk copolymers and attached thereto side chains of another polymeric material. Such copolymers are old in the art, for example, the graft copolymers disclosed in the following U.S. Pat. Nos.: 3,136,738; 3,539,664; 3,644,571 and 3,673,277. The graft copolymers of the prior art, however, were difficult to prepare in pure form and contained substituents that could form crosslinks or unreacted trunk polymers and side-chain polymers. The graft copolymers are useful, for example, as films, molded or extruded objects as well as coatings. While some of the graft copolymers disclosed in the aforementioned patents have an ethylene/maleic anhydride backbone polymer, the graft copolymers can be distinguished. U.S. Pat. No. 3,136,738, in Example 16, describes the preparation of a graft copolymer of a 50:50 ethylene/maleic anhydride and caprolactam, wherein more than a 100-fold excess of caprolactam is present. That example illustrates a noncrystallizable trunk copolymer and a polyamide content of more than 99 percent. U.S. Pat. No. 3,539,664, in Example 7, describes the polymerization of caprolactam, a 31:69 ethylene/maleic anhydride copolymer and omega-amino-caproic acid. A homogeneous composition was achieved. The composition of the patent contains a higher ratio of maleic anhydride in the polymer backbone and contains longer side chains as evidenced by a melting point of 215.degree.C.; the composition having high stiffness and moisture resistance. U.S. Pat. No. 3,644,571 describes a composition having a low level of an olefin:maleic anhydride polymer backbone with polyamide side chains wherein the percentage of polyamide in the graft copolymer is at least 96 percent by weight. U.S. Pat. No. 3,673,277 discloses plastics prepared from copolymers of ethylene and maleic anhydride and particular noncrystalline polyamide which are crosslinkable to form thermosetting plastics.